Method for preparing aerogel and aerogel slurry, and aerogel and slurry prepared thereby

Abstract

The present invention relates to a process for preparing aerogels and aerogel slurries, and aerogels and slurries prepared thereby. More particularly, the present invention relates to an eco-friendly process for preparing aerogels and aerogel slurries in which carbon dioxide is used as a reactant and consumed in the process.

Description

[0001] The present invention relates to methods for preparing aerogels and aerogel slurries, and to aerogels and slurries prepared thereby. More particularly, the present invention relates to environmentally friendly methods for preparing aerogels and aerogel slurries, in which carbon dioxide is used as a reactant and consumed in the process.

[0002] Aerogels are porous materials with a high specific surface area, which have a wide range of commercial applications in different industries such as construction, insulation, catalysis, and drug delivery. For example, aerogels can be used as aggregates in cement applications to provide lightweight and insulating properties, while aerogel slurries can be used to paint buildings or as waterproof coatings for various applications.

[0003] Aerogels are typically manufactured via a sol-gel process, in which a three-dimensional "wet gel" skeleton is obtained, followed by a solvent exchange step to replace the original sol-gel solvent in the wet gel pores with a drying solvent. In the final step, drying is carried out to produce a porous aerogel structure. Aerogel slurries are typically prepared from porous aerogels, for example by mixing the porous aerogel with a wet binder, and then preparing the aerogel via the above route (i.e., via the steps wet gel (WG) to aerogel (A) to aerogel slurry (AS)).

[0004] Conventional methods for preparing aerogels are not environmentally friendly and typically result in the emission of CO2 and air pollutants, and / or the use of toxic volatile organic compounds or acids. For example, when supercritical drying is used in the drying step, a large amount of CO2 needs to be flushed through the aerogel. When ambient drying techniques are used, a large amount of volatile organic compounds are released, and even those techniques that rely on water-based solvents for drying (Han et al., Bioinspired Synthesis of Monolithic and Layered Aerogels, Advanced Materials: 2018, 30(23)) result in the emission of CO2 as a by-product. These drawbacks also mean that the production of aerogels is limited to environments where trained technicians and safety procedures for handling hazardous materials are in place.

[0005] The use of CO2 as a gelling agent in the preparation of silica aerogels has been reported (Wu et al., Silica Aerogels formed from Soluble Silicates and Methyltrimethoxysilane (MTMS) using CO2 gas as a gelation agent, Ceramics International: 2018, 44, 821 - 829). In this process, sodium silicate (water glass), CO2, and water react to form a silica wet gel. However, the sodium carbonate by - product is removed by washing with water, so CO2 is not used as part of the aerogel product but is removed as an effluent in wastewater.

[0006] More environmentally friendly methods for preparing aerogels are known, such as the method described by Plank et al. (Plank et al., Preparation and Characterisation of a Calcium Carbonate Aerogel, Research Letters in Materials Science: 2009, 1 - 3). However, this method uses supercritical drying, has the disadvantages mentioned above, and the resulting calcium carbonate aerogel has lower fire resistance, lower porosity, and higher density compared to conventional silica aerogels.

[0007] The object of the present invention is to avoid or reduce one or more of the disadvantages associated with the prior art. An environmentally friendly method for preparing aerogels and aerogel slurries would be useful as it would allow for an overall reduction in CO2 emissions or even net - zero CO2 emissions. A method with reduced processing or drying time and / or that can be carried out at ambient temperature and is scalable would be particularly beneficial as it would be a direct route to obtaining an aerogel slurry, which avoids the need to prepare the finished aerogel and then incorporate it into the slurry. A method that avoids the need for hazardous chemicals and allows it to be carried out without specialized equipment and / or in a non - laboratory environment would be useful.

[0008] Overview

[0009] The present invention relates to methods for preparing aerogels and aerogel slurries, and the aerogels and slurries prepared thereby. Both the preparation of aerogels and aerogel slurries via the methods of the present invention consume CO2 as a reactant and retain the CO2 in the resulting aerogel or slurry product, thereby providing significant environmental benefits compared to prior art methods that typically emit CO2. In embodiments, the present invention provides a direct route for preparing aerogel slurries from wet gels (i.e., WG to AS). Advantageously, the methods of the present invention avoid the use of toxic volatile organic solvents or strong acids and provide a simple, energy-efficient, and environmentally friendly process for preparing both aerogels and aerogel slurries. In certain aspects, the method can be carried out in a home or non-laboratory environment due to the lack of volatile or hazardous liquid chemicals and the need for specialized equipment.

[0010] Accordingly, the present invention relates to a method for preparing a silica or alumina wet gel for use in preparing an aerogel or an aerogel slurry, the method comprising:

[0011] providing a precursor solution comprising an alkylsilane and / or a metal alkoxide, and reacting the precursor solution in the presence of a sol-gel solvent to form a reaction mixture;

[0012] and adding a gelling agent to the reaction mixture,

[0013] to form a wet gel,

[0014] wherein the gelling agent is an alkaline earth metal oxide solid.

[0015] Accordingly, in a first aspect of the present invention, there is provided a method for preparing a silica or alumina wet gel for use in preparing an aerogel or an aerogel slurry, the method comprising:

[0016] providing a precursor solution comprising an alkylsilane and / or a metal alkoxide, and reacting the precursor solution in the presence of a sol-gel solvent to form a reaction mixture having a pH from 3 to 9;

[0017] and adding a gelling agent to the reaction mixture,

[0018] to form a wet gel,

[0019] wherein the gelling agent is an alkaline earth metal oxide solid.

[0020] The gelling agent is added in its alkaline earth metal oxide solid form, i.e., it is not formed in situ.

[0021] The reaction mixture has a pH from 3 to 9. The method does not use an acid. In embodiments, the reaction mixture does not include an acid. Advantageously, the method avoids the use of an acid, and particularly a strong acid, which was previously considered necessary in the preparation of silica gels.

[0022] In an embodiment, the reaction mixture has a pH ranging from 3 to 7.

[0023] In an embodiment, the reaction mixture has a pH ranging from 4 to 9.

[0024] In an embodiment, the reaction mixture has a pH ranging from 4.5 to 9.

[0025] In an embodiment, the reaction mixture has a pH ranging from 5 to 8.75.

[0026] The wet gel contains a silica (silicon dioxide) or alumina gel framework and an alkaline earth metal hydrated solution containing an alkaline earth metal hydroxide.

[0027] The alkaline earth metal oxide solid can be selected from calcium oxide, magnesium oxide, barium oxide, and strontium oxide.

[0028] In an embodiment, the alkaline earth metal solid is calcium oxide.

[0029] In an embodiment, the alkaline earth metal solid is added to the reaction mixture at a molar concentration of 0.002 M to 195 M.

[0030] In an embodiment, the alkaline earth metal solid is added to the reaction mixture at a molar concentration of 0.002 M to 20 M.

[0031] In an embodiment, the alkaline earth metal solid is added to the reaction mixture at a molar concentration of 0.01 M to 2 M.

[0032] In an embodiment, the precursor solution contains an alkylsilane.

[0033] The alkylsilane can be selected from methyltriethoxysilane (MTES) and methyltrimethoxysilane (MTMS). A mixture of alkylsilanes can also be used.

[0034] In an embodiment, the alkylsilane is methyltriethoxysilane (MTES).

[0035] In an embodiment, the precursor solution contains a metal alkoxide.

[0036] The metal alkoxide can be selected from tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), polyethoxydisiloxane (PEDS), and aluminum tri-sec-butoxide. A mixture of metal alkoxides can also be used.

[0037] In an embodiment, the precursor solution contains an alkylsilane and a metal alkoxide.

[0038] In an embodiment, the metal alkoxide is in liquid form.

[0039] In an embodiment, the sol-gel solvent comprises an alcohol.

[0040] Suitable alcohols are known to those skilled in the art and include, but are not limited to, C1-C4 alcohols, ethanol, methanol, propanol, and butanol.

[0041] In an embodiment, the sol-gel solvent is a mixture of water and an alcohol.

[0042] In an embodiment, the sol-gel solvent is a mixture of carbonated water and an alcohol.

[0043] In an embodiment, the alcohol is ethanol, and preferably bioethanol. "Bioethanol" means ethanol produced in an environmentally friendly manner, for example, by fermenting biomass containing sugar and starch components such as plant by-products.

[0044] In an embodiment, in the sol-gel solvent, the molar ratio of water or carbonated water: alcohol ranges from 100:1 to 1:100, from 50:1 to 1:50, or from 20:1 to 1:20. In an embodiment, the ratio is from 10:1 to 1:10, or from 5:1 to 1:5.

[0045] The method includes reacting a precursor solution in the presence of a sol-gel solvent. When the precursor solution reacts in the presence of a sol-gel solvent, it can be used at a molar ratio of precursor: sol-gel solvent of from 100:1 to 1:100, from 50:1 to 1:50, or from 20:1 to 1:20. In an embodiment, the ratio is from 10:1 to 1:10, or from 1:4 to 1:10.

[0046] The present inventors have advantageously demonstrated that when an alkaline earth metal oxide solid is used as a gelling agent, a wet gel is formed that comprises a silica (silicon dioxide) or alumina gel framework and an alkaline earth metal hydrate solution. The excess alkaline earth metal oxide solid and its alkaline earth metal hydroxide product can react with carbon dioxide to form the corresponding alkaline earth metal carbonate, which is retained in the final aerogel or aerogel slurry product. Advantageously, unlike other processes that use CO2 (e.g., as a gelling agent as described by Wu et al., where CO2 is used and then released as a by-product), in the process of the present invention, the alkaline earth metal oxide and its hydroxide product in the wet gel can react with CO2 and consume CO2, and the CO2 is retained in the final aerogel or aerogel slurry product in the form of a carbonate. This means that the production of aerogels and aerogel slurries results in a net consumption of CO2, which has significant environmental advantages when atmospheric CO2 is used. For example, in the case where CaO is used as the alkaline earth metal solid, 1 mole of CO2 is captured by 1 mole of CaO to produce 1 mole of CaCO3, and the CaCO3 is retained or trapped in the final aerogel or aerogel slurry product. CO2 can be introduced before gelation (e.g., by adding carbonated water to the reaction mixture, as part of the sol-gel solvent or otherwise) and / or after gelation (e.g., in an aging step).

[0047] In a first aspect of the present invention, the wet gel prepared by the method of the present invention can be used to prepare an aerogel or an aerogel slurry.

[0048] When the wet gel is used to prepare an aerogel slurry, the method can include the step of blending the wet gel to form a slurry mixture.

[0049] The wet gel can be blended by any suitable means, such as by crushing the gel using a spoon or a stirrer, by mechanical means or any other suitable means apparent to those skilled in the art. As those skilled in the art will understand, although the blending step is not essential, blending the wet gel breaks up the gel and exposes more surface area for further reaction.

[0050] In an embodiment, the method includes adding a desiccant and optionally water to the slurry mixture.

[0051] In an embodiment, the desiccant can be an alkaline earth metal oxide. The alkaline earth metal oxide solid used as the desiccant can be the same as the alkaline earth metal oxide solid used as the gelling agent; however, this is not required, and in an embodiment, different alkaline earth metal solids can be used. This can be advantageous for imparting desired properties to the resulting aerogel product.

[0052] In an embodiment, the desiccant is an alkaline earth metal solid selected from calcium oxide, magnesium oxide, barium oxide, and strontium oxide.

[0053] Advantageously, the alkaline earth metal oxide solid reacts exothermically with the water in the pores of the wet gel in the slurry mixture, and this exothermic reaction can cause the slurry to self-heat and promote drying. If desired or needed, additional water can be added to maximize the exothermic reaction and speed up the drying time. Any residual water can be absorbed by the by-product hydroxide.

[0054] In an embodiment, the desiccant is calcium oxide.

[0055] The desiccant can be added to the wet gel at a molar concentration ranging from 0.016 M to 162.114 M.

[0056] The desiccant can be added to the wet gel at a molar concentration ranging from 0.016 M to 35 M.

[0057] The desiccant can be added to the wet gel at a molar concentration ranging from 0.016 M to 20 M.

[0058] In an embodiment, the method further includes introducing carbonated water into the reaction mixture, and / or introducing carbon dioxide into the wet gel or into the wet slurry mixture or dry slurry mixture; to form an aerogel or an aerogel slurry.

[0059] In an embodiment, the step of introducing carbon dioxide into the wet gel or into the wet slurry mixture or dry slurry mixture includes introducing CO2 gas or exposing the wet gel or slurry mixture to atmospheric CO2.

[0060] In an embodiment, carbon dioxide gas is introduced into the wet gel or slurry mixture. Although high-purity CO2 or industrial CO2 can be used, i.e., introduced into the wet gel or slurry mixture from a tank or by similar suitable means, advantageously, the CO2 can be sourced from the atmosphere. In this embodiment, the wet gel or slurry mixture can be exposed to the atmosphere and aged. In an embodiment, the aging occurs at ambient temperature and ambient pressure. During the aging step, CO2 reacts with the alkaline earth metal hydroxide to form the corresponding carbonate, and the carbonate is trapped within the pores of the aerogel and within the pores and around the silica skeleton of the aerogel slurry.

[0061] In an embodiment, the CO2 in the carbonated water or added to the wet gel or slurry mixture reacts with the alkaline earth metal hydroxide to form a carbonate, and the carbonate remains in the aerogel or aerogel slurry.

[0062] In an embodiment, when preparing the aerogel, the method further includes a step of drying the wet gel or the aged wet gel to form the aerogel. In an embodiment, the method includes one or more drying steps. The drying step can be carried out by conventional means, such as in an oven or on a hot plate. Suitable heating methods will be apparent to those skilled in the art. In an embodiment, the drying step can be selected from subcritical drying, ambient pressure drying, supercritical drying, and freeze drying. Subcritical drying techniques and ambient pressure drying techniques may be preferred because of their low environmental impact.

[0063] In an embodiment, the drying step includes heating at ambient pressure.

[0064] The heating can be carried out at a temperature from 60 °C to 500 °C. In an embodiment, the heating is carried out from 60 °C to 150 °C.

[0065] A temperature of about 100 °C (e.g., from 80 °C to 120 °C) may be preferred because the liquid phase has a boiling point not higher than 100 °C.

[0066] The drying step can be carried out for a duration from 15 minutes to 24 hours. As will be understood by those skilled in the art, the duration of the drying step will depend on the heating temperature, where a lower temperature requires a longer drying time. In an embodiment, the drying step is carried out for a duration from 15 minutes to 12 hours or from 15 minutes to 6 hours. In an embodiment, the drying step is carried out for a duration from 20 minutes to 3 hours or from 30 minutes to 2 hours. When the drying temperature is in the range from 60 °C to 150 °C, the drying time can be from 30 minutes to 12 hours, from 30 minutes to 8 hours, from 30 minutes to 6 hours, or from 30 minutes to 2 hours.

[0067] Since the aerogel slurry has undergone a drying step before aging with CO2, the aerogel slurry product does not require a separate drying step. However, if desired, a subsequent drying step can be carried out because the dried slurry product exhibits different water affinity characteristics, as discussed in more detail below.

[0068] In an embodiment of the present invention, the aerogel can be prepared with fibers to allow the preparation of fiber-reinforced products. In these embodiments, the fibers can be added during the step of forming the wet gel, i.e., by adding the fibers when reacting the precursor solution in the presence of a sol-gel solvent; and adding a gelling agent. Alternatively or additionally, the fibers can be added at a later stage, for example when blending the wet gel to form a slurry. Suitable fibers for the method of the present invention include ceramic fibers, organic fibers, carbon fibers, and glass fibers.

[0069] In an embodiment, the fiber is a ceramic fiber. Triton TMCeramic short fibers are illustrative examples of fibers that can be used. In an embodiment, the fibers are glass fibers. A 6 mm glass fiber bundle is another illustrative example of fibers that can be used. Those skilled in the art will understand that these examples are illustrative and alternative fibers can be used.

[0070] Advantageously, when using fibers, the method of the present invention allows for the rapid production of reinforced aerogels or aerogel slurry composites. The term composite is used to describe an aerogel having one or more additional components, such as fibers that can be introduced into the aerogel structure.

[0071] Drawings

[0072] The present invention will now be described by way of example only with reference to the drawings, in which:

[0073] Figure 1 A reaction schematic for preparing an aerogel according to an embodiment of the present invention is shown;

[0074] Figure 2 A reaction schematic for preparing an aerogel slurry according to an embodiment of the present invention is shown;

[0075] Figure 3 An elastic test of the aerogel prepared in Example 1.2 is shown;

[0076] Figure 4 The results of X-ray diffraction on the aerogel prepared in Example 1.2 are shown;

[0077] Figure 5 An SEM image of the aerogel prepared in Example 1.2 is shown;

[0078] Figure 6 The aerogel slurry prepared in Example 3.2 after drying is shown;

[0079] Figure 7 The results of X-ray diffraction on the aerogel slurry (after drying) prepared in Example 3.2 are shown;

[0080] Figure 8 An SEM image of the aerogel slurry (after drying) prepared in Example 1.2 is shown;

[0081] Figure 9 A photograph of the aerogel prepared in Example 2 is shown;

[0082] Figure 10 A photograph of the fiber-reinforced aerogel prepared in Example 4 is shown.

[0083] Detailed description

[0084] Now refer to Figure 1 Describing the embodiments of the present invention in detail, Figure 1 The preparation of an aerogel according to the present invention is schematically illustrated. Figure 1 In the step of preparing the wet oxide gel, a sol-gel process is performed using a precursor and a solvent. The precursor is an alkylsilane, a metal alkoxide, or a mixture thereof. The sol-gel solvent is a mixture of an alcohol and water, such as a mixture of bioethanol and water. In certain embodiments, CO2 can be introduced into this step, for example, in the form of carbonated water. Carbonated water can be part of the sol-gel solvent. No acid is used in the reaction mixture, and the pH range of the reaction mixture is from 4 to 9.

[0085] Figure 1 In the sol-gel step, the wet gel reaction results in the formation of a wet oxide gel, which comprises an oxide gel skeleton and an alkaline earth metal hydrate solution. Both during the sol-gel step and after the wet oxide gel is formed, the alkaline earth metal solid (e.g., Figure 1 calcium oxide in) and its hydroxide products (e.g., Figure 1 The calcium hydroxide in the ) captures carbon dioxide and reacts with it to form alkaline earth metal carbonates, such as Figure 1 1 mole of CO2 is captured by 1 mole of CaO to produce 1 mole of CaCO3. The CO2 may be high purity CO2 or industrial CO2, such as that introduced from a tank, or preferably may be CO2 from the atmosphere to which the reaction is exposed.

[0086] The carbonates formed are trapped within the pores of the aerogel, which means that CO2 is consumed during the process and, unlike prior art methods, CO2 is retained within the aerogel rather than released. This has significant environmental benefits and allows the method to act as a carbon capture and utilization process. The method can use atmospheric CO2 as a direct air capture technology. The aerogel can then be dried using any conventional drying means, such as ambient pressure drying, subcritical drying, supercritical drying, freeze drying, etc. to form the final aerogel product.

[0087] Therefore, the steps can be summarized as:

[0088]

[0089] In the above scheme, CO2 is introduced into the system during the aging step and reacts with the alkaline earth metal oxide and its hydroxide product in the wet gel to form carbonates, which are retained in the final aerogel and aerogel slurry product. However, alternatively or additionally, CO2 can be introduced before the gelation stage, for example by introducing carbonated water into the reaction mixture. When carbonated water is introduced into the reaction mixture, carbonated water can be used, for example, in the sol-gel solvent.

[0090] Now, embodiments of the present invention in which a wet gel is used to prepare an aerogel slurry will be described with reference to Figure 2 . In Figure 2 , a wet oxide gel is obtained by a sol-gel process carried out in the same manner as described in Figure 1 using a precursor and a solvent. The precursor is an alkylsilane, a metal alkoxide, or a mixture thereof. The sol-gel solvent is a mixture of an alcohol and water, such as a mixture of bioethanol and water (or alternatively carbonated water may also be used). The reaction mixture does not include an acid and has a pH ranging from 4 to 9.

[0091] Figure 2 . In

[0092] , the wet gel reaction results in the formation of a wet oxide gel that contains an oxide gel skeleton and an alkaline earth metal hydrate solution. Then, an alkaline earth metal oxide solid is added to the formed wet oxide gel to act as a desiccant. The alkaline earth metal oxide solid reacts with the water in the pores of the wet oxide gel in an exothermic reaction, which can cause the slurry mixture to self-heat and promote drying. If desired or necessary, additional water may be added to maximize the exothermic reaction and accelerate the drying time. Any residual water can be absorbed by the by-product hydroxide. Figure 2 Figure 2 Figure 2 . The alkaline earth metal solid (e.g., calcium oxide in Figure 2 ) and its hydroxide product (calcium hydroxide in

[0093] ) in the slurry mixture can capture carbon dioxide and react with carbon dioxide to form the corresponding alkaline earth metal carbonate (e.g., calcium carbonate in Figure 2

[0094] ). The CO2 can be high-purity CO2 or industrial CO2, such as high-purity CO2 or industrial CO2 introduced from a cylinder, or preferably it can be CO2 from the atmosphere to which the reaction is exposed. The formed carbonate is trapped within the pores of the slurry and around the silica skeleton, which means that CO2 is consumed during the process and, unlike prior art methods, CO2 remains in the final product rather than being released. This has significant environmental benefits. Additionally, this method allows for the direct preparation of an aerogel slurry, i.e., preparing an aerogel slurry (AS) from a wet gel (WG), without the need to prepare an aerogel product according to conventional methods and then mix it with a wet binder. This has significant benefits in terms of commercialization and scale-up. The wet slurry can be directly used in coating applications, such as for painting and the like.

[0093] Alternatively, the wet slurry can be dried and used in the form of a dry slurry. If drying is required, the aerogel slurry can be dried using known techniques, such as ambient pressure drying, subcritical drying, supercritical drying, freeze drying, etc. Due to environmental benefits, ambient pressure and ambient temperature may be preferred for any optional drying step.

[0094] Therefore, the steps can be summarized as follows:

[0095]

[0096] In the above scheme, CO2 is introduced into the system during the aging step and reacts with the alkaline earth metal oxides and their hydroxide products in the wet gel to form carbonates, which are retained in the final aerogel and aerogel slurry products. However, alternatively or additionally, CO2 can be introduced before the gelling stage, for example, by introducing carbonated water into the reaction mixture. When carbonated water is introduced into the reaction mixture, it can be used in the sol-gel solvent.

[0097] The method of the present invention will now be described by way of example only. Examples:

[0098] Materials:

[0099] Methyltriethoxysilane (MTES 99%) was purchased from Hubei Kofule Material Technology Co., Ltd., China. Bioethanol (ethanol, 96.6%) was purchased from Bioethanol Fireplace, UK. Calcium oxide (CaO 99%) was purchased from MineralsWater, UK. Carbon dioxide (CO2 100%) gas was purchased from AUTOart, UK. The carbonated water used was Aqua Vale TM Sparkling Spring Water.

[0100] Methodology:

[0101] The pH was directly measured using a Vleoak pH meter with a high precision of 0.01 and a measurement range of 0 - 14.

[0102] Example 1:

[0103] 1.1 Preparation of wet gel :

[0104] MTES was used as a precursor and mixed with a sol-gel solvent composed of bioethanol and water, where the molar ratio of MTES, bioethanol, and water was 1:8:22. The pH of the reaction mixture was measured and determined to be 8.75. CaO powder was added as a gelling agent to the precursor mixture liquid at a molar concentration of 0.016M.

[0105] 1.2 Preparation of aerogel from wet gel:

[0106] The silica wet gel prepared in Example 1.1 was aged in gaseous CO2 by covering the container containing the wet gel with plastic wrap and blowing CO2 from a tank into the container. The aging was carried out for 7 days.

[0107] Finally, the aged wet gel was directly dried at 100 °C in a sealed container for 2 hours to produce silica aerogel.

[0108] Based on 1 mole of CaO capturing 1 mole of CO2, the CO2 captured in this process was theoretically determined to be 0.013 g CO2 / gram of silica aerogel produced.

[0109] 1.3 Characterization of aerogel 1.3.1

[0111] The bulk density of the aerogel of Example 1.2 was calculated from the measured weight / measured volume and determined to be 0.08 g / cm 3 .

[0112] The porosity of the aerogel was calculated from the bulk density using the following equation:

[0113] Porosity = (1 - (bulk density / theoretical density)) * 100

[0114] It was determined to be 96%.

[0115] The flexibility of the aerogel was demonstrated by manual compression, as Figure 3 shown.

[0116] The hydrophobicity of the aerogel was measured using open-source analysis (Stalder et al., “Low-Bond Axisymmetric DropShape Analysis for Surface Tension and Contact Angle Measurements of Sessile Drops”, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2010), where the product exhibited a contact angle of 141°.

[0117] The X-ray diffraction of the aerogel was performed using Empyrean powder XRD with Cu radiation at a scan rate of 1.3° / min and a step size of 0.02°. As a result, it is shown in Figure 4 that the aerogel product contains amorphous silica gel as the main component, and calcium carbonate (CaCO3) is also present, as demonstrated by the peak at 29.5°.

[0118] SEM imaging was performed using a Zeiss 500 scanning electron microscope-field emission gun to image the samples at an acceleration voltage of 5 keV in high vacuum mode. Before SEM imaging, all samples were coated with gold to increase conductivity. The results are shown in Figure 5It is shown, and a transparent nanoporous structure composed of a silica framework is shown.

[0119] Example 2:

[0120] 2.1 Preparation of wet gel

[0121] MTES was used as a precursor and mixed with a sol-gel solvent composed of bioethanol and carbonated water (pH 4.6), where the molar ratio of MTES, bioethanol, and water was 1:8:22. The pH of the reaction mixture was measured and determined to be 5.14. CaO powder was added as a gelling agent to the precursor mixture liquid at a concentration of 0.016 M.

[0122] 2.2 Preparation of aerogel from wet gel:

[0123] The silica wet gel prepared in Example 2.1 was aged in gaseous CO2 by covering the container containing the wet gel with plastic wrap and blowing CO2 from a tank into the container. The aging was carried out for 7 days.

[0124] Finally, the aged wet gel was directly dried in a sealed container at 100 °C for 2 hours to produce a silica aerogel.

[0125] Based on 1 mole of CaO capturing 1 mole of CO2, the CO2 captured in this process was determined to be 0.013 g CO2 / gram of silica aerogel.

[0126] 2.3 Characterization of aerogel 2.3.1

[0128] The bulk density of the aerogel of Example 2.2 was calculated by measured weight / measured volume and determined to be 0.089 g / cm 3 .

[0129] Example 3:

[0130] 3.1 Preparation of wet gel :

[0131] MTES was used as a precursor and mixed with a sol-gel solvent composed of bioethanol and water, where the molar ratio of MTES, bioethanol, and water was 1:8:22. The pH of the reaction mixture was measured and determined to be 8.75. CaO powder was added as a gelling agent to the precursor mixture liquid at a molar concentration of 0.016 M.

[0132] 3.2 Direct preparation of aerogel slurry from wet gel (WG to AS):

[0133] The obtained silica wet gel was blended to disrupt the gel structure and form a slurry, which was then mixed with 5.9 g of CaO as a desiccant. The drying was promoted by both the desiccant property of CaO and the exothermic reaction between CaO and water, which dried the internal pores. After mixing with CaO, the outer surface of the slurry began to warm up (increasing between 2 °C and 5 °C). After one hour, the external temperature of the slurry had returned to the ambient temperature, leaving a partially dried slurry that still appeared wet. Once the step of mixing the slurry with the alkaline earth metal solid as a desiccant was completed, the aging step was carried out by covering the container holding the dried slurry mixture with plastic wrap and blowing CO2 from a tank into the container. The aging was carried out for 7 days, at which time an aerogel slurry was obtained without the need for further drying steps.

[0134] In this example, once the drying of the internal pores occurred and a partially dried slurry was obtained, the aging step was carried out. However, as those skilled in the art will understand, the aging step can be started at any point in time after the addition of the alkaline earth metal solid desiccant.

[0135] Based on 1 mole of CaO capturing 1 mole of CO2, the CO2 captured in this process was theoretically determined to be 1.56 g CO2 / gram of the produced silica aerogel slurry.

[0136] 3.3 Characterization of aerogel slurry

[0137] To characterize the wet gel, the slurry was first dried in air at ambient pressure and ambient temperature without any additional heating for 14 days.

[0138] The bulk density of the dried aerogel slurry of Example 3.2 was calculated from the measured weight / measured volume and determined to be 0.04 g / cm 3 。

[0139] The porosity of the aerogel slurry was calculated from the bulk density using the following equation:

[0140] Porosity = (1 - (bulk density / theoretical density)) * 100

[0141] It was determined to be 85%.

[0142] Figure 6 is a photograph of the dried slurry showing the external structure of the dried slurry. The dried slurry shows the overall properties, i.e., the dried slurry was found to be porous with a biscuit-like texture. The overall properties indicate that the formed calcium carbonate acts as a binder in the aerogel slurry.

[0143] The hydrophilicity of the aerogel was measured using open-source analysis (Stalder et al., “Low-Bond Axisymmetric Drop Shape Analysis for Surface Tension and Contact Angle Measurements of Sessile Drops”, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2010), where the product had a contact angle of 80°.

[0144] X-ray diffraction was performed using Empyrean powder XRD with Cu radiation at a scan rate of 1.3° / min and a step size of 0.02°. As a result, it is shown in Figure 7 that the aerogel product contains amorphous silica gel, where calcium carbonate (CaCO3) is the main component, and amorphous silica gel is also present.

[0145] SEM imaging was performed using a Zeiss 500 scanning electron microscope - field emission gun to image the samples at an acceleration voltage of 5 keV in high vacuum mode. Before SEM imaging, all samples were coated with gold to increase conductivity. The results are shown in Figure 8 It is shown that a nanoporous microstructure was achieved and it was demonstrated that the formed calcium carbonate was involved in the resulting structure. The method of the present invention can be used to prepare silica wet gel or alumina wet gel for preparing aerogel or aerogel slurry. The method has many advantages and in particular consumes CO2, which is extremely beneficial from an environmental perspective. The method also avoids the use of volatile chemicals and does not require specialized equipment, allowing the method to be used in domestic and commercial environments. For example, the method can be used to prepare render in situ at a residential or construction site. In an embodiment, the method can be used to directly prepare aerogel slurry from wet gel (i.e., WG to prepare AS), avoiding the need for intermediate preparation of aerogel and then mixing the aerogel with a wet binder.

[0146] Example 4:

[0147] 4.1 Preparation of wet gel :

[0148] MTES was used as a precursor and mixed with a sol-gel solvent composed of bioethanol and water, where the molar ratio of MTES, bioethanol, and water was 1:8:22. The pH of the reaction mixture was measured and determined to be 8.75. CaO powder (1.6 g) was added as a gelling agent to the precursor mixture liquid at a molar concentration of 0.016 M. Additionally, 2.36 g of short ceramic fibers (Triton TMKaowol Epsilon ceramic fiber, pure, Fisher Chemical TM )。

[0149] 4.2 Preparation of aerogel from wet gel:

[0150] The fiber-reinforced silica wet gel prepared in Example 4.1 was aged in gaseous CO2 by covering the container containing the wet gel with plastic wrap and blowing CO2 from a cylinder into the container. The aging was carried out for 7 days.

[0151] Finally, the aged fiber-reinforced wet gel was directly dried in a closed container at 100 °C for 2 hours to produce a fiber-reinforced silica aerogel.

[0152] Based on 1 mole of CaO capturing 1 mole of CO2, the CO2 captured in this process was theoretically determined to be 0.013 g CO2 / gram of the produced fiber-reinforced silica aerogel.

[0153] All features disclosed in this specification (including any accompanying claims, abstract and drawings) and / or all steps of any method or process so disclosed may be combined in any combination, except combinations in which at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by an alternative feature serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is only an instance of a general series of equivalent or similar features. The invention is not limited to the details of the foregoing embodiments. The invention extends to any novel feature or any novel combination of features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel step or any novel combination of steps of any method or process so disclosed.

[0154] Regarding the use of substantially any plural and / or singular terms herein, the skilled person can convert from the plural to the singular and / or from the singular to the plural, where appropriate for the context and / or application. For clarity, various singular / plural permutations may be set forth explicitly herein.

[0155] Those skilled in the art will understand that, generally speaking, the terms used herein, and especially the terms used in the appended claims, are generally intended to be "open" terms (e.g., the term "including" should be understood as "including but not limited to", the term "having" should be understood as "having at least", the term "includes" should be understood as "including but not limited to", etc.). Those skilled in the art will further understand that if a specific number is intended to be introduced in the claim statement, such intention will be explicitly stated in the claim, and in the absence of such a statement, there is no such intention. For example, for the sake of understanding, the following appended claims may contain the use of introductory phrases "at least one" and "one or more" to introduce claim statements. However, the use of such phrases should not be construed to mean that introducing a claim statement by the indefinite article "a" or "an" will limit any particular claim containing such an introduction to an embodiment containing only one such statement, even when the same claim includes introductory phrases "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should be interpreted to mean "at least one" or "one or more"); the same applies to the use of the definite article to introduce a claim statement. In addition, even if a specific number of the introduced claim statement is explicitly stated, those skilled in the art will recognize that such a statement should be interpreted to mean at least the stated number (e.g., merely stating "two statements" without any other modifiers means at least two statements or two or more statements).

[0156] It will be understood that, for purposes of illustration, various embodiments of the present disclosure have been described herein and various modifications can be made without departing from the scope of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, and the true scope is indicated by the appended claims.

Claims

1. A method for preparing a silica or alumina wet gel for preparing an aerogel or an aerogel slurry, the method comprising: A precursor solution containing an alkylsilane and / or a metal alkoxide is provided and the precursor solution is reacted in the presence of a sol-gel solvent to form a reaction mixture having a pH from 3 to 9; and a gelling agent is added to the reaction mixture, to form a wet gel, wherein the gelling agent is an alkaline earth metal oxide solid.

2. The method according to claim 1, wherein the alkaline earth metal oxide solid is selected from calcium oxide, magnesium oxide, barium oxide and strontium oxide.

3. The method according to claim 1 or claim 2, wherein the precursor solution comprises an alkylsilane selected from methyltriethoxysilane (MTES) and methyltrimethoxysilane (MTMS); a metal alkoxide selected from tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), aluminum tri-sec-butoxide and polyethoxydisiloxane (PEDS); and mixtures thereof.

4. The method according to any one of the preceding claims, wherein the sol-gel solvent comprises an alcohol.

5. The method according to claim 4, wherein the sol-gel solvent is a mixture of an alcohol and water or a mixture of an alcohol and carbonated water.

6. The method according to claim 4 or claim 5, wherein the alcohol is selected from ethanol, methanol, propanol and butanol.

7. The method according to any one of the preceding claims, wherein the silica or alumina wet gel is used for preparing an aerogel slurry, and the method further comprises the step of blending the wet gel to form a slurry mixture.

8. The method according to claim 7, wherein the method comprises adding a desiccant and optionally water to the slurry mixture.

9. The method according to claim 8, wherein the desiccant is an alkaline earth metal oxide solid.

10. The method according to claim 9, wherein the desiccant is calcium oxide.

11. The method according to any one of the preceding claims, wherein the method further comprises introducing carbonated water into the reaction mixture according to any one of claims 1 to 6, and / or introducing carbon dioxide into the wet gel according to any one of claims 1 to 6 or into the slurry mixture according to any one of claims 7 to 10 to form an aerogel or an aerogel slurry.

12. The method according to claim 11, wherein the step of introducing carbon dioxide into the wet gel or into the slurry mixture comprises introducing CO2 gas into the wet gel or the slurry mixture, or exposing the wet gel or the slurry mixture to atmospheric CO2.

13. The method according to any one of the preceding claims, wherein the method comprises adding fibers.

14. The method according to claim 13, wherein the step of reacting the precursor solution in the presence of the sol-gel solvent and adding the gelling agent to form a wet gel; and / or the step of blending the wet gel to form a slurry mixture; is carried out in the presence of fibers.

15. The method according to claim 13 or claim 14, wherein the fibers are ceramic fibers, organic fibers, carbon fibers or glass fibers.

16. The method according to any one of claims 11 to 15, wherein the method further comprises drying the aerogel.

17. A kit comprising: alkylsilane and / or metal alkoxide; alkaline earth metal oxide solid; alcohol; and instructions for carrying out the method according to any one of claims 1 to 16.

18. A method for capturing CO2 in silica or alumina aerogel or aerogel slurry, the method comprising reacting CO2 with an alkaline earth metal solid during the preparation of silica or alumina aerogel or aerogel slurry to obtain alkaline earth metal carbonate trapped in the pores of the aerogel or aerogel slurry product.

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